Electronic Warfare (EW) includes, but is not limited to, the following:
Electronic Counter Measures (ECM) This is the active use of the electromagnetic spectrum to deny its use by the enemy. Most ECM activity is in the form of jamming.
Electronic Counter Counter Measures (ECCM) This is all activities related to making enemy ECM activites less successful. It includes technical modification to radio equipment (such as frequency-hopping spread spectrum), the education of radio operators (enforcing strict discipline) and modified battlefield tactics.
Electronic Support Measures (ESM) This is the passive use of the electromagnetic spectrum to gain intelligence about other parties on the battlefield. This intelligence might be used directly as fire missions for artillery or air strike orders, or as the basis of ECM/ECCM actions.
ECM and most of ECCM actions can be detected by the enemy by nature of their active use of transmissions. ESM, however, can be conducted without the enemy ever knowing it. Its strategic counterpart, SIGINT and COMINT is continuously perfomed by most of the world's countries in order to gain intelligence about potential enemies' electronic equipment and tactics.
